The human Lamin B receptor (LBR) belongs to the ERG4/ERG24 family of nuclear envelope inner membrane proteins. It anchors the lamina and the heterochromatin to the inner nuclear membrane. LBR can interact with chromodomain proteins. LBR has an amino-terminal domain of approximately 200 amino acids followed by a carboxyl-terminal domain that is similar in sequence to yeast and plant sterol reductases. Two LBR-like genes have recently been identified in humans which have strong carboxyl-terminal domains of LBR and sterol reductases (Pezhman et al. (1998) Genomics 54(3):469-476). The human LBR/sterol reductase like proteins are localized to the endoplasmic reticulum. These LBR/sterol reductase proteins may define a human gene family encoding proteins of the inner nuclear membrane and endoplasmic reticulum that function in nuclear organization and/or sterol metabolism.
In the nucleus LBR undergoes phosphorylation by CDC2 protein kinase in mitosis when the inner nuclear membrane breaks down into vesicles that dissociate from the lamina and the chromatin. It is phosphorylated by different protein kinases in interphase when the membrane is associated with these structures. Phosphorylation of LBR proteins may be responsible for some of the alternations in chromatin organization and nuclear structure which occur at various times during the cell cycle. To date, a Lamin B receptor has not been identified in plants. A plant Lamin B receptor could be used to manipulate cell cycle regulation and plant transformability.
Accordingly, the availability of nucleic acid sequences encoding all or a portion of these proteins would facilitate studies to better understand transcritional regulation, cell cycle progression, and developmental events in eucaryotic cells. It would also provide genetic tools for the manipulation of cell cycle regulation and increase the efficiency of transformation.